Allergy Basics

Overview

Allergies arise when the immune system overreacts to factors in the environment that are normally harmless. There are a variety of environmental factors that can induce an allergic reaction, leading to various symptoms and degrees of severity. Some allergies are minor and barely noticeable, while other allergic reactions can be life threatening. Although there is no “cure all” for allergies, there are various ways to alleviate the symptoms.

The immune system

The immune system is basically a collection of specialized cells that detect and destroy agents that could potentially be harmful to the body, such as bacteria, viruses, cancer cells, yeast, etc.

• One of the most important parts of the immune system is the bloodstream cells.
• The bloodstream contains both red and white blood cells.
• Red blood cells function primarily to carry oxygen to cells throughout the body
• White blood cells function primarily to fight off potentially harmful agents.
• Some white blood cells produce proteins that specifically recognize potentially harmful agents. These specialized proteins are known as antibodies.
• Antibodies are composed of molecular structures known as immunoglobulin, of which there are several varieties.
• One type of immunoglobulin is immunoglobulin E (IgE). IgE’s are the type of antibodies associated with allergies.
• IgE antibodies attach to mast cells, located in the eyes, throat, nose, lungs, gastrointestinal tract, and in the skin.
• IgE recognizes normally harmless certain factors and reacts to their presence as if they were harmful. These factors are known as allergens.
• Each IgE antibody detects one specific allergen.
  

When an allergen is detected by an IgE antibody

• The IgE antibody sends a signal to the mast cell to which it is attached.
• This mast cell secretes histamine and other chemicals, leading to inflammation characteristic of many allergic reactions.
• Allergic rhinitis – inflammation of the mucous membrane lining the nose, commonly known as “hay fever”
• Hives (urticaria) – itchy, swollen welts that last for minutes to days
• Angiodema – swelling around eyes and lips (sometimes hands and feet)
• Asthma – inflamed airways become constricted, making it more difficult to breath. Symptoms include:

• Wheezing
• Coughing
• Chest tightness
• Shortness of breath
• Eczema – inflammation of the skin
• Contact dermatitis – occurs after an allergen comes into contact with the skin
  

No one is sure what exactly leads to the development of allergies, but allergies do tend to be inherited. Therefore, if you have a family history of allergies, you are more likely to develop allergies.

Allergic response

The specific variety and severity of an allergic response to an environmental agent can vary greatly among individuals. Allergies can be grouped by the antagonist allergen and the severity of allergic response. Allergies can be grouped into respiratory allergies, food allergies, skin allergies, insect bite allergies, and drug allergies. There are also three grades of allergy severity: mild, moderate and severe.

Mild

• Symptoms are localized
• Can include rash, hives, itchy watery eyes, nasal congestion
  

Moderate

• Symptoms spread to other parts of the body
• Can include itching that spreads, difficulty breathing
  

Severe

A severe allergic reaction is known as Anaphylaxis. The symptoms can spread quickly throughout the body, and in severe cases can be life threatening if breathing is obstructed and/or if blood pressure drops a lot. Bee stings, certain foods (such as nuts) and certain drugs (such as penicillin) most commonly cause Anaphylaxis. Symptoms include:

• Swelling of the face, throat, mouth
• Tingling of mouth or throat
• Difficulty swallowing or breathing, wheezing
• Stomach Cramps
• Vomiting
• Diarrhea
• Hives
• Quick drop in blood pressure
• Dizziness, loss of consciousness
• Restlessness and anxiety
  

Respiratory Allergies

Respiratory allergies are often caused by air allergens. These allergens generally affect the eyes, nose and lungs. The allergic response is often triggered when the allergen comes into contact with the mucous membrane (lining) of the nose. The allergic response often includes inflammation and swelling of the lining of the nose and eyes. Although there are a variety of air allergens that can trigger an allergic response, the symptoms of those allergies are often similar.

Common air allergens

• Pollen – often the cause of “seasonal allergies”
• Dust mites – microscopic insects that live in fibers that are not often laundered, such as bedding, upholstery, carpet, etc.
• Mold – a fungus that grows in damp areas, such as basements and bathrooms, and releases spores; it is usually the spores that cause an allergic reaction.
• Animal dander - proteins in animal dander or saliva
  

Allergic response

• Sneezing
• Nasal congestion
• Watery eyes
• Itchy eyes, mouth, nose and/or throat
• Asthma symptoms
  

Food Allergies

Most people with food allergies are children. Most symptoms occur minutes within an hour after eating the food. An allergic reaction can affect the mouth, stomach and intestines. Food that induces an allergic reaction contains proteins that are not broken down by the digestion process and enter the bloodstream through the intestine. Thus, symptoms of food allergies can become apparent throughout the body.

It is common for people to mistake food allergies with food intolerance or even food poisoning, since the symptoms may be similar. One of the more common examples of food intolerance is lactose intolerance, where an individual does not have enough lactase, an enzyme found in the intestines, to effectively breakdown the lactose in milk. As a result, indigestion may occur, which is also one of the symptoms of food allergy.

Common food Allergens

Children

• Peanuts
• Milk
• Eggs
• Soybeans
• Wheat
  

Adults

• Peanuts
• Tree nuts
• Shellfish
• Fish
• Eggs
  

Other

• Berries
• Some food additives
  

Allergic Response

• Asthma symptoms
• Nasal congestion
• Swelling around mouth, face, tongue
• Stomach cramps
• Vomiting
• Diarrhea
• Rash
• Itching of skin
• Hives
• Nausea
• Anaphylaxis

Insect bite allergies

When an individual gets stung by some insects, that insect injects venom into the site of the sting. While the venom usually produces redness, swelling and itchiness, some individuals react particularly severely to these bites and then suffer from more severe symptoms.

Insects that most commonly induce an allergic response

• Bees
• Wasps
• Hornets
• Yellow Jackets
• Fire ants

Allergic Response

• Red hives
• Itchy rash
• Swelling of the face, throat, mouth or area of sting
• Wheezing, difficulty breathing
• Difficulty swallowing
• Nausea
• Abdominal pain
  

Insect stings or bites are the most common cause of anaphylaxis.

Skin Allergies

The skin can show signs of an allergic reaction and become inflamed and irritated as a result. The antigens can reach the mast cells of the skin either from the environment (e.g. contact with latex) or from the bloodstream (e.g. digested food allergen). Allergic skin reactions can also be associated with other types of allergies, such as respiratory allergies.

Common Allergens

• Latex
• Extreme temperatures
• Certain foods
• Drugs
• Allergic rhinitis
• Certain chemicals
• Certain metals (e.g. nickel)
• Poisonous plants
• Emotional stress
  

Allergic Response

• Itching of the skin or nose
• Redness of the skin
• Hives
• Rashes
• Scaling
  

Latex allergy can result in:

• Itchy watery eyes
• Nasal congestion
• Asthma
• Anaphylaxis
  

Drug Allergies

People can sometimes develop allergies toward certain drugs by producing antibodies to fight that specific drug. Whenever the drug is taken, the antibodies can induce an allergic reaction.

Drugs that most commonly induce an allergic reaction

• Penicillin and related antibiotics
• Aspirin
• Sulfa drugs
• Barbiturates
• Iodine
• Local anesthetics
  

Allergic Response

• Hives
• Skin rash
• Itchy skin
• Itchy eyes
• Nasal congestion
• Swelling of the mouth and/or throat
• Anaphylaxis
  

Diagnosis and tests

Skin testing

A scratch test is done in order to determine if one has antibodies targeted for a suspected allergen. A dilute amount of allergen is placed on the back or forearm, and then the site is scratched. This allows the potential allergen to enter the skin, thus exposing the mast cells to the solution. If IgEs specific for that substance are present on the mast cells, the mast cells will be triggered to release histamine, thus causing the skin to become inflamed (redness, swelling). Such a reaction is considered a positive test result.

Blood testing

A blood sample can be taken and examined using a radioallergosorbent test (RAST). The RAST can test to see if certain IgE antibodies are present and in the blood. People with allergies will generally have elevated levels of IgE antibodies in their blood. The test cannot determine the severity of allergies, and is not as accurate as some other allergy tests.

Food Challenge

A food challenge is performed in order to test whether or not one is allergic to a specific food. A capsule containing the potential food allergen is ingested, and the patient will be observed for an allergic reaction. Several capsules of different food allergens may be ingested in this manner to rule out other potential allergens, and to control for foods known not to induce allergies. In a double-blind test, both the doctor and the patient will not know which potential allergen is in the capsule.

Treatments to control the symptoms of allergies

• Antihistamines – drugs that target histamines, thereby preventing the chemical from triggering an inflammatory response
• Steroids – a drug that reduces inflammation
• Epinephrine (adrenalin) – a hormone that is an effective treatment for anaphylaxis, and must be injected
• Immunotherapy (allergy shots or allergy desensitization) – by injecting small amounts of allergens, the body will become more tolerant of that allergen
• Avoiding factors that may cause or exacerbate allergies
• Stress – stress can exacerbate allergy symptoms
• Vacuuming
• Air conditioning and air filters can reduce airborne allergens
• Use dust mite covers over the mattress
• Foods known to cause allergic symptoms
• Substances or materials that cause allergic symptoms